Castiel has never really found it in his heart to love a human like he does you. He will do anything for you which scares him. After the boys helped (y/n). (y/n) became interested in hunting. After stumbling upon the lost angel she begins research and try's to help. After giving up (y/n) looks to the winchesters for help. When meeting up with them she realizes that the three were a team before and has reunited them. Struggling to understand everything (y/n) try's to have a normal life. But the angel will not leave her alone. He is grateful towards you and wants to protect you. He loves you. Thus a dynamic duo was created. You made him fall, he is your Fallen Angel.